High-rolling son of a high diver

The Irish entrepreneur Denis O'Brien made his fortune in telecoms in the 1990s, but his career has latterly been defined by his confrontation with Sir Anthony O'Reilly. O'Brien is one of Ireland's leading business people and has worked with most of the others - from serial entrepreneur and former London City airport owner Dermot Desmond to Ryanair founder Tony Ryan and the packaging magnate Michael Smurfit.

But he has clashed with O'Reilly after amassing a stake in his prized asset, Independent News & Media, owner of the Independent. O'Brien first locked horns with O'Reilly - one of the most high-profile and richest businessmen in Ireland - in 1995 when both bid for Ireland's second mobile phone licence. Backed by international investors, the young upstart's Esat won.

Those were friendlier times and O'Reilly offered the young entrepreneur his congratulations, reminding him that he had known O'Brien's father, a champion high diver, and saying he did him credit.

The next decade saw the relationship sour as O'Brien sought to take bites out of the older man's empire. According to Forbes, O'Brien replaced O'Reilly as Ireland's third-richest person last year. O'Brien, who is 50 and married with four children, is worth £1.6bn.

Born in Dublin, the son of a veterinary supplier, O'Brien's school career showed little promise but after studying history and politics at University College Dublin, he went on to an MBA course at Boston College and a career in Irish radio. But it was his dramatic Esat mobile licence win in 1995 that made him.

O'Brien floated Esat in 1997, then got more than £300m by selling most of it to BT while retaining a 30% stake. He now runs a highly successful mobile business in the Caribbean, Digicel, and has radio interests in Ireland and across Europe.